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View Full Version : What does cache mean?




rye9
May 22, 2006, 04:29 PM
What does it mean when an iPod fills its cache? Is it good or bad? Apple.com says an iPod fills its cache every 25 minutes... what does that mean, you shouldn't use it for too long? :o



WildCowboy
May 22, 2006, 04:32 PM
No. The cache is the amount of data it can store separate from the hard drive. For Apple's advertised encoding methods, the iPod holds 25 minutes of music in the cache...this is like skip protection in case the hard drive is unable to be read due to vibrations. It also saves battery life because the power-intensive spinning up of the hard drive only occurs every 25 minutes (in theory) instead of having constant hard drive access.

rye9
May 22, 2006, 04:35 PM
OK, so the first 25 minutes of songs are "skip-protected", that's what it means, right?

WildCowboy
May 22, 2006, 04:40 PM
OK, so the first 25 minutes of songs are "skip-protected", that's what it means, right?

Sort of...it's not just the first 25 minutes. The cache (which is RAM) is capable of holding up to 25 minutes worth of songs (at 128 kbps AAC). So when you start up your iPod, the hard drive will spin up and load 25 minutes of songs into RAM. It can play that amount of music without having to go back to the hard drive for more data. But the hard drive will periodically spin up to allow the iPod to refill the cache as you progress through the playlist.

Constantly navigating through playlists limits the ability of the iPod to use cache (because it's constantly having to change what's coming next, and thus reloading the cache with new data), which results in more hard drive access, which decreases battery life.

rockthecasbah
May 22, 2006, 04:42 PM
OK, so the first 25 minutes of songs are "skip-protected", that's what it means, right?
yes, but it is more so in regards to making the Hard Drive spin less, prolonging battery life. Rather than having to spin up to load each song, it sets up a virtual cue getting multiple songs from one spin-up. Since the HD is already spinning (which starting takes the most power) it is more battery-friendly to save these songs and spin less.